Scissors usually are made by connecting two cutting blades through a rotatable pivot and adjusting the shear between the blades. They cut an object by placing the object between the blades and closing the blades. A structure is created enabling one contact point to reliably move from the bases to the tips to enable an object gripped between the joined parts to be cut. This system is the same both with large sizes and small sizes. The “adjustment of shear” is the work of grinding the blades by a grindstone to give the target rate of curvature at the time of honing and setting the dimensions so that the shear point “smoothly” advances to the tips by a constant force with the opposite side blade. Since it is difficult to make exactly the same blade from the way of making the two blades, so this shear adjustment work has been considered essential. This shear adjustment work has a direct impact on the cutting ability of the scissors. Paper cutting scissors and other scissors for general applications are generally made by machining, but high quality scissors, for example, medical use scissors, are often made by hand. Such scissors are given sharpness and durability by the skill of the manufacturer. For this reason, “shear adjustment” has been considered to require experience and intuition.
Hair cutting scissors have blade lengths of 50 mm to 150 mm or so. The grindstones used are also disk shaped ones of 300 mm or so in diameter. The shear adjustment work can be said to be relatively easy work since both hands are used and therefore force can be easily applied. On the other hand, medical use scissors sometimes only have blade lengths of 10 to 30 mm. There are also further smaller ones for a special use having blade lengths of only 2 mm. Therefore, manufacture currently relies on the skill of the craftsmen.
In the present circumstances, scissors have usually been made using the same grade of material for the left and right blades. They are adjusted by shear adjustment when creating bending, torsion. Usually, they are made so that the maximum performance is obtained when new. Along with use, the two blades bend and the torsion becomes off, the blades are worn down, and other abnormalities occur. To keep this to a minimum, the blades have been heat treated or made to plastically deform to try to maintain the shape.
Further, in conventional scissors, including medical use scissors, the pivot, fulcrum, and force point correspond to the screws, crescents, and blades, respectively. Blade with slight curves are screwed together to be able to rotate. The resistance received when the blade cut (resistance keeping the blades open when starting to cut) is received at the crescent, that is, the parts where the two blade slide against each other at the inner surfaces of the blades at the opposite sides to the screw. It limits movement of the blade and enables cutting. The crescents start to receive surface pressure starting from when cutting an object. As the cutting proceeds toward the tips of the blades, the pressure becomes larger, but the area corresponding to the crescents also increases.
FIG. 8 to FIG. 13 show the structures of conventional scissors. In each structure, the one ends of the pair of shanks form an upper shear blade and lower shear blade, the other ends of the pair of shanks form handles, and the handles are opened and closed around a pivot at which the shanks intersect so as to open and close the upper shear blade and the lower shear blade. The upper shear blade and the lower shear blade are generally made from the same grade of steel. FIG. 8 shows one example of conventional medical use scissors where the tip sides are curved upward. In the figure, 11 indicates the upper shear blade, 12 the lower shear blade, 3 the pivot, 41 and 42 shanks, and 51 and 52 handles. The pair of shanks 41 and 42 cross at the pivot 3.
FIG. 9 shows the names of the parts of general scissors. In the perspective view (a), the upper shear blade is indicated by 11, the lower shear blade by 12, the fulcrum (pivot or shaft) by 3, the shanks by 41, 42, and eye rings by 43. Furthermore, cutting edges 14, bases 15, tips 16, back 17, and crescents 18 are the main elements forming the scissors. (b) is a partial view of the area around the pivot, while 19 is a pivot hole.
FIG. 10 is a schematic view of general scissors when the blades are closed and shows a lateral view. General scissors in the closed state generally strictly have a clearance between the two cutting edges of the upper shear blade and the lower shear blade.
FIG. 11 is a schematic view of the state where the blades are open in the same scissors and shows a lateral view. In the open state, strictly speaking generally the tips intersect as shown in the lateral view.
FIG. 12 schematically shows the outer surface side (a) and inner surface side (b) of one blade (11 or 12). At the outer surface side, a blade ridge is formed. At the inner surface side, crescent 18 is formed near pivot hole 19 on the shank side. The cutting edge is formed at the location where the outside surface and the inside surface of the blade intersect and has a sharpness enabling an object to be cut at a location contacting the cutting edge of the opposite side blade. Blades 11 and 12 are fastened to be able to rotate by being screwed or swaged together at pivot 3. For this reason, blades 11 and 12 are provided with pivot holes 19.
FIG. 13 shows schematic views of scissors with the tip sides curved upward used for medical use etc. (a) is a perspective view, (b) is a lateral view, and (c) is a plan view. The tip sides of the two blades are curved upward, but the structure is basically the same as normal flat blade.